1. Field of the Invention
The field of the invention relates generally to fiber optic modal multichannel duplex devices which may be useful, for instance, in fiber-optic communication systems and fiber optic sensing systems. More specifically, the field of the invention may be generally described as a novel method and apparatus for providing a wedge-shaped fiber optic dielectric waveguide structure for optical fiber ends for radiating and/or modulating standing waveguide modes and linearly polarized modes for use in systems in which optical fibers of any type, including but not limited to single mode, few mode and multimode fibers, are utilized to communicate information or to utilize the physical characteristics of the optical fiber to provide a number of sensing functions such as, for instance and not by way of limitation, measuring temperature by analyzing the Raman scattering of photons and other sensing applications. A novel apparatus and method for mechanically polishing optical fibers to achieve the dielectric waveguide wedge endface and lip of the invention is also disclosed and claimed.
2. Background Art
Significant research energy is being expended in field of fiber optic modal multiplexing and de-multiplexing. The typical focus of research is directed at developing an ability to communicate digital data through the dielectric waveguide. Similar focus has been directed toward the ability of the dielectric waveguide modes to respond to various sensor system stimuli. Previous work performed by Lan Truong (Florida Institute of Technology) and Sachin Narahari Dekate (Florida Institute of Technology) demonstrated that modal de-multiplexing and multiplexing is possible. However, the common processes by which the optical fiber structures are currently fabricated is hazardous, was not consistently repeatable and require significant experience to refine the process to provide a working optical fiber capable of radiating modal rings.
Previous work in the field of fabricating structures to produce radiated modal rings from optical fibers have relied upon a dangerous process using highly caustic chemicals in which hydrofluoric acid solutions are typically used to etch the tips of optical fibers into a cone shape. These chemicals require a very tight material safety data sheet (MSDS) and storage control, which can be very costly and may be prohibitive to the facilities and handling requirements. In addition to storing the chemicals, disposing of the chemicals is dangerous and costly. The use of such harsh chemicals as hydrofluoric acid makes the methods of the prior art inefficient, unreliable, hazardous and costly for mass production.
Fiber-optic communication and sensing systems are generally known in the art: such systems have been known to comprise optical fibers further comprising end shapes created by a chemical etching process, resulting in a cone shaped optical fiber tip designed to radiate modal rings from few mode fibers. Such fiber ends have historically been created by a hydrofluoric or other acid etching processes which may be characterized as non-repeatable, expensive, difficult to achieve, and utilizing a chemical process that is not friendly to the environment. Etching of an optical fiber tip creates a cone shape in which the core of the fiber is etched to a very fine point, which can be problematic. With most few mode fiber cores measuring at 8.4 microns, any vibration, sudden air currents, physical manipulation or tapping of the optical fiber can result in breakage of the fiber tip. If the tip is broken the modal ring radiation is lost. The hydrofluoric etching process cannot be expected to achieve a six sigma manufacturing process and is thus not adaptable to a production environment, or even to a laboratory environment where repeatability is important. A simpler more repeatable process is required to ensure the modal ring technology is able to transition into commercial applications for use industry.
One process for hydrofluoric acid flow etching of conical fiber tapers is described in Hydrofluoric acid flow etching of low loss sub wavelength diameter by conical fiber tapers, Eric J. Zhang et al., Department of Electrical and Computer Engineering and the Institute for Optical Sciences, University of Toronto, Toronto, Ontario M5S3G4, Canada (“Zhang et al.”). Zhang et al. describes An etch method based on surface tension driven flows of hydrofluoric acid microdroplets for the fabrication of low-loss, subwavelength-diameter bi-conical fiber tapers is presented. Tapers with losses less than 0.1 dB/mm were demonstrated, corresponding to an order of magnitude increase in the optical transmission over previous acid-etch techniques. The etch method produces adiabatic taper transitions with minimal surface corrugations. However, it is obvious from the text of Zhang et al. that the processes described therein for chemically etching optical fibers is not mass-repeatable, economic, or environmentally friendly as is typical of the acid-based optical fiber etching processes known in the art.
What is needed in the art, therefore, is an economic, repeatable, highly reliable and environmentally friendly method and structure for creating optical fiber modal multichannel duplex devices that may be utilized to modulate an excitation source by amplitude, phase and/or frequency in single mode, few mode, and multimode fiber optic communications and sensing systems. The present invention provides such features by creating a unique wedge and lip shaped optical dielectric waveguide end face using a novel and repeatable mechanical polishing method, all of which is claimed.